Atmospheric Turbulence and Solar Diameter Measurement

Irbah, Abdenour; Bouzid, Abderrezak; Lakhal, Lyès; Seghouani, N.; Borgnino, J.; Delmas, Christian; Laclare, F.

doi:10.1007/3-540-45755-0_7

Cited by 2 publications

(2 citation statements)

References 32 publications

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“…The main source of error is the atmospheric turbulence and the true difficulty is to distinguish between the variations due to the atmosphere and those of true solar origin. A more complete study of the atmospheric effects on solar diameter measurements has been made by Irbah et al (2003) who show that the observation conditions have more impact on the errors than on the measurements of the diameter mean value. Even if the data are certainly affected by the turbulence effects, it would be unlikely that rather similar results found by different observers on different sites (and using different techniques) would not reflect a real solar effect.…”

Section: Solar Radius Ground-based Observationsmentioning

confidence: 99%

Solar latitudinal distortions: From observations to theory

Lefebvre¹,

Rozelot²

2004

A&A

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Abstract. Solar diameters have been measured from different ground-based instruments on different sites all around the world.There are values dating back to three centuries ago, but the revival of interest began in the 1970s when it was claimed that a temporal periodic modulation had been found. The interest of such measurements, pinpointed from only two decades, may not lie in these temporal variations, but in the fact that a latitudinal heliographic dependence may exist. Such a solar shape distortion has been deduced from the analysis of solar astrolabe data sorted by heliographic latitudes, but observational evidence has also been obtained by means of a scanning heliometer (Pic du Midi Observatory). Latitudinal dependence implies sub-surfacic physical mechanisms and can be explained theoretically. Thus, in spite of the fact that ground-based observations are altered by seeing effects that may amplify or superimpose noise, it can be advanced that the solar shape is not a pure spheroid. We present here a new theory based upon the thermal-wind equation, which explains the observed distorted solar shape. Using the W parameter (called here asphericity-luminosity parameter), we show that large negative values (W ranging from around −0.075 up to −0.6) leading to a prolate Sun, are unlikely. The best range of W lies between around −0.075 and +0.6. Concerning observations, only space missions (or balloon flights) will be able to reach a clear conclusion. A space mission called PICARD is scheduled to be launched by 2008: one of its major aims is to measure these asphericities with astrometric precision.

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Section: Solar Radius Ground-based Observationsmentioning

confidence: 99%

Solar latitudinal distortions: From observations to theory

Lefebvre¹,

Rozelot²

2004

A&A

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“…Many works have been devoted to this subject, the main issue being to know how to deconvolute the observed data by an adequate function which expresses the state of the atmosphere at the time of the observation. One can see for instance [Hill et al, 1975, Rozelot et al, 2003or Irbah et al, 2003. Thanks to the new instrumentations at the Calern Observatory (South France) which will permit to observe in real time both the solar and the atmospheric signals, it will be possible in a near future to extend the series obtained from space.…”

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confidence: 99%

How big is the Sun: Solar diameter changes over time

Rozelot¹,

Kosovichev²,

Kılçık³

2018

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: The measurement of the Sun's diameter has been first tackled by the Greek astronomers from a geometric point of view. Their estimation of ≈ 1800″, although incorrect, was not truly called into question for several centuries. The first pioneer works for measuring the Sun's diameter with an astrometric precision were made around the year 1660 by Gabriel Mouton, then by Picard and La Hire. A canonical value of the solar radius of 959″.63 was adopted by Auwers in 1891. In spite of considerable efforts during the second half of the XXth century, involving dedicated space instruments, no consensus was reached on this issue. However, with the advent of high sensitivity instruments on board satellites, such as the Michelson Doppler Imager (MDI) on Solar and Heliospheric Observatory (SoHO) and the Helioseismic and Magnetic Imager (HMI) aboard NASA's Solar Dynamics Observatory (SDO), it was possible to extract with an unprecedented accuracy the surface gravity oscillation ƒ modes, over nearly two solar cycles, from 1996 to 2017. Their analysis in the range of angular degree l = 140 -300 shows that the so-called "seismic radius" exhibits a temporal variability in anti-phase with the solar activity. Even if the link between the two radii (photospheric and seismic) can be made only through modeling, such measurements provide an interesting alternative which led to a revision of the standard solar radius by the International Astronomical Union in 2015. This new look on such modern measurements of the Sun's global changes from 1996 to 2017 gives a new way for peering into the solar interior, mainly to better understand the subsurface fields which play an important role in the implementation of the solar cycles.

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Atmospheric Turbulence and Solar Diameter Measurement

Cited by 2 publications

References 32 publications

Solar latitudinal distortions: From observations to theory

Solar latitudinal distortions: From observations to theory

How big is the Sun: Solar diameter changes over time

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